What Does a Good Weld Look Like? Visual Signs, Defects & Inspection Guide

Introduction: Why Learning to Read a Weld Matters

You finish a bead, flip up your helmet, and stare at the joint. The edges look a little ragged, a few tiny holes glint in the light, and one side of the fillet is noticeably fatter than the other. Is this a weld you can trust, or one that will crack the first time it sees real load? Every welder has stood in that exact spot, squinting and second-guessing.

That moment is why “what does a good weld look like” gets asked by far more than beginners. Inspectors, engineers, and fabricators ask a version of it every single day. A hobbyist wants to know if their practice bead is finally acceptable. A quality engineer wants to know if a fabricated assembly can ship. The question sounds simple, but the answer depends on what you can see, what you can’t, and what the job actually requires.

Throughout this guide, we look at a weld through three lenses:

• Appearance: what you can see at the surface, from bead shape and uniformity to toe lines and spatter.
• Soundness: the internal quality hidden beneath the surface.
• Code compliance: whether the weld meets the applicable acceptance criteria.

One pair of terms trips up almost everyone, so let’s settle it early. A discontinuity is simply any interruption in the typical structure of the material, like a bit of porosity, a small undercut, or an inclusion. A defect is different. It is a discontinuity that, by its nature or accumulated effect, exceeds the acceptance criteria and makes the part rejectable. In other words, a discontinuity isn’t automatically bad; it only becomes a defect when it fails to meet the standard.

That’s why the American Welding Society recommends that acceptance standards be clearly understood by both the manufacturer and the buyer before welding starts. Agreeing on those rules up front avoids the argument that happens later, when one side calls a weldment satisfactory and the other refuses it.

Here’s the honest truth about looking. Visual examination is fast, inexpensive, and remarkably powerful, and it’s where every inspection begins. The AWS B1.11M/B1.11 Guide for the Visual Examination of Welds is built on exactly that idea. But eyes alone can’t see inside a joint. Lack of penetration, internal porosity, slag inclusions, and internal cracks are all invisible from the outside. Finding those requires nondestructive testing: ultrasonic, radiographic, penetrant, or magnetic particle methods.

So this article walks through what a good bead actually looks like, then compares results by process, including how to read good and bad MIG welds. From there we cover the defects that hide behind a pretty surface, the limits of visual inspection, and how to read your own settings from the bead you just laid. To keep your eyes safe while you study every one, it helps to know your protective eyewear.

By the end, you’ll have a practical framework: judge appearance, respect soundness, and always ask which acceptance criteria apply. Reading a weld well is a skill you build bead by bead.

The Anatomy of a Good Weld Bead: Shape, Size, and Profile

Think of a weld bead the way you’d think of a bridge. It isn’t enough that it exists and holds weight — the shape decides where stress piles up and where cracks eventually begin. Weld geometry is that shape. Get the profile right and the joint shrugs off load for decades. Get it wrong and a bead that looks perfectly acceptable can fail far below its rated strength.

Two joint families dominate here: fillet welds and groove welds. Each has its own geometry to read, though process matters too — our Good and Bad MIG Welds: How to Tell the Difference guide shows how the same rules play out with wire feed.

Fillet Welds: Leg Length, Throat, and Symmetry

A fillet weld sits in the corner where two members meet. Its size is described by leg length — how far the bead reaches along each plate — and throat thickness, the shortest distance from the weld face to the root. Those are the dimensions the engineer used to calculate how much load the joint can safely carry. If the bead comes out undersized, that calculation no longer applies.

A healthy fillet looks like a right triangle with a gently rounded hypotenuse, sitting evenly in the corner. A good bead is centered between the two members rather than covering more of one side than the other. That imbalance is called asymmetry, and it’s a real defect indicator — heat and filler went where they shouldn’t, usually because the torch was tilted or aimed off the root. A symmetric bead melts into both plates equally and builds the full specified leg on each side. To see how wire-feed machines behave on joints like these, read How to Use a Wire Welder: Complete Beginner’s Guide.

Groove Welds: Reinforcement and Penetration

On a groove weld, the bead fills a channel between two plates butted together. Good geometry means full penetration — fusion all the way to the root — and controlled reinforcement, the slight mound of weld metal sitting above the plate surface. Reinforcement should be modest and even. Too little leaves the joint flush or sunken and reduces the throat; too much stacks weld metal that adds stress concentration without adding usable strength. A quick glance at a finished groove weld should show a flat-to-slightly-crowned face that blends cleanly into both edges.

The Toe Transition: Where Fatigue Cracks Begin

The toe is the line where the bead meets the base metal, and its angle matters enormously. A good toe transitions smoothly, like a gentle ramp. Steep, near-vertical sides are a warning sign: they mean the bead sits higher than it needs to, and every sharp corner becomes a stress raiser. Under repeated loading, fatigue cracks almost always start at a sharp toe. This is one reason welding standards such as ISO 5817 pay so much attention to weld contour rather than just size.

Overfill, Convexity, Concavity, and Underfill

These four words describe how the face of the bead is shaped, and each one is a message:

• Convexity — a bead that bulges up like a loaf of bread. A little crowning is normal and healthy. Too much traps stress at the toes and often hides incomplete fusion underneath.
• Concavity — a face that dips inward like a valley. It looks tidy but thins the throat, the load-bearing section of the weld.
• Overfill — excess weld metal piled above the surface, creating a heavy, lumpy crown.
• Underfill — a face sitting below the surrounding base metal, leaving a groove that reduces cross-section and invites cracks.

Inspection programs grade welds in tiers. Outstanding fillet welds show uniform leg length, convexity under 1/16 in., and consistent bead width. Unacceptable ones show convexity or concavity greater than 1/8 in. — clear signals that something in the setup or technique went wrong. AWS D1.1 acceptance guidance also caps undercut at roughly the lesser of 1/32 in. or 5% of material thickness on statically loaded plate welds, so even a small toe notch has a defined limit.

Here’s the part that surprises many beginners: weld profile is reported to cause more weld failures than internal flaws in some program quality references. A bead can be structurally sound inside and still fail because its contour concentrates stress. Next time you look at your bead, compare its outline to the smooth, symmetric, moderate profile above — plain language and a trained eye are your first inspection tools.

Reading the Surface: Uniformity, Ripples, Toe Lines, and Spatter

Once a bead is cool, its surface is a written record of everything your torch did. You don’t need X-ray eyes to catch most trouble — the covering tells the story. The trick is knowing which surface features are normal and which are red flags. Reading a bead well is a learnable skill, and it pays off across every process you run.

Start with Straightness and Uniform Width

A good weld bead runs straight and follows the joint without wandering side to side. Its width stays consistent along the whole length, with no thin spots, bulges, or gaps where the puddle starved out. Think of the trailing edge as a set of railway tracks: if the bead drifts, your travel angle or hand steadiness needs work. A wandering bead is rarely a mystery — it almost always traces back to inconsistent travel speed, a shaky grip, or a torch angle that keeps changing mid-run.

In multi-pass welds, look at how the beads stacked. A high-quality weld has consecutive beads overlapping each other by roughly 25–50%, with the toe of each new bead landing near the center of the previous one. Uniform, deliberate stacking also helps control heat buildup, which keeps distortion and residual stress in check. Uneven overlap can bury slag or create a cold lap — a defect covered in detail in this guide to overlap welding defects.

What the Ripple Pattern Tells You

The ripples — often called “stacked dimes” — are the frozen fingerprint of your travel speed and heat input. The shape is diagnostic:

• Narrow, V-shaped ripples: usually mean the weld ran too hot, flattening the bead and widening the toes.
• Wide, C-shaped ripples: point to too cold a setting or too slow a travel speed.
• Even, consistent C-shaped ripples: the goal. Evenly spaced ripples that stay the same the entire length signal steady travel speed and stable heat.

Rhythm matters as much as shape. A weld that looks great for two inches then blurs into mush usually means the operator sped up as the part heated. Consistency is the whole game here: a single lapse in pace shows up as a blemish long before it ever becomes a failed weld. Suppliers often publish bead photos worth comparing against — Wiley Metal’s guide to good weld bead characteristics is a solid reference.

Spatter, Toe Lines, and Arc Strikes

Spatter is tiny molten droplets that cooled outside the puddle. A little is normal, but excessive spatter around the bead usually means wire feed speed and voltage weren’t in the optimal range. Flux-cored processes throw more spatter than TIG, but it should still be light and easily removable. If it’s welded on tight, revisit your settings — this flux-core polarity guide helps you match DCEN versus DCEP to the job.

Now scan for arc strikes: localized remelted or heat-affected spots where a stray arc touched the metal outside the joint. These are classified as defects and often require repair or removal, because the rapid quench can leave hard, crack-prone zones. Also watch for “chicken tracks” or “wagon tracks” — the parallel grooves left when slag or porosity rides up the bead edges.

A Practical Visual Checklist

Run through this after every bead:

1. Bead runs straight and follows the joint line.
2. Width is uniform — no thin or fat sections.
3. Ripples are evenly spaced and consistent in shape.
4. Toe lines blend smoothly into the base metal with no undercut.
5. No surface porosity, pinholes, or visible cracks.
6. Spatter is minimal and easy to knock off.
7. No arc strikes, wagon tracks, or burn marks.
8. Stainless shows only light, acceptable temper colors.

Get in the habit of comparing your bead against a known-good sample. The skill builds fast — and pairing that eye with the right technique, like the ones in this MIG weld comparison guide, sharpens both together.

Good vs. Bad Welds Across Processes: MIG, TIG, Stick, and Flux-Cored

Every arc process lays down metal its own way, so a “good” bead under a MIG gun looks nothing like a good bead under a TIG torch. Judge a weld against the wrong process and you’ll either flag a perfectly sound joint or excuse a bad one. Here’s what quality actually looks like in each of the four big arc processes — and where the real dividing line sits — before we get into the details.

MIG (GMAW): Smooth and Tidy When Dialed In

Once voltage and wire feed speed are optimized, MIG leaves minimal spatter and a smooth, slightly convex bead with fine, even ripples. That tight, uniform rippling is the fingerprint of a stable arc and steady travel speed. A heavy spatter shower, a bead sitting up like a caterpillar, or a wandering toe line usually points back to settings or technique rather than the process itself. Because the wire feeds continuously and the arc stays short, small changes upstream show up fast on the bead face. For a side-by-side breakdown, read Good and Bad MIG Welds.

TIG (GTAW): The Cleanest Bead of the Bunch

TIG produces the cleanest, most uniform beads of any arc process: no spatter, tight “stacked dime” ripples, and a bright, silvery, controlled face. Because there’s no flux or slag, the weld surface is essentially the finished weld. It only dulls or discolors when heat input or shielding gas coverage is off. That cleanliness is why TIG dominates on stainless, aluminum, and thin material, and why a single bad bead stands out so clearly. If you’re setting up the machine, this guide on AC or DC for TIG welding explains the polarity choices.

Stick (SMAW): Rougher, Thicker, Slag-Covered

Stick is the rough-and-tumble option. Expect thicker reinforcement, coarser ripples, more spatter, and a slag coating that must be chipped before you can inspect anything. A sound stick weld can look lumpy and still pass, so don’t judge it by smoothness alone. Look for consistent bead width, even edges, and full coverage during the pass — then chip and check for uniform ripples and no undercut. Dial in the electrode with these 3/16 E7018 amperage and technique notes.

Flux-Cored (FCAW): MIG-Like, But Messier

FCAW resembles MIG because both feed wire continuously, but flux-core is slag-covered and tends to throw more spatter. Fabricators commonly report incomplete fusion at the root, slag inclusions, rope-like beads, and alternating “chicken tracks” across the weld face. Those chicken-track patterns are often a travel-speed or voltage symptom. Elongated piping porosity can mean electrode extension is too short; increasing electrode extension lowers amperage and typically clears the problem. Polarity matters too, so understanding DCEN vs DCEP for flux core is worth the read. Comparing the two wire processes? See Is Flux Core the Same as MIG?, and if you’re new to wire feeding, start with How to Use a Wire Welder.

At-a-Glance Comparison

The Standard Isn’t the Style

Here’s the catch: beauty is process-specific, but acceptance isn’t. The real pass/fail line comes from the applicable code, such as ISO 5817 for steel fusion welds or AWS D1.1 for structural steel. A code doesn’t care whether your bead is a perfect stack of dimes or a rugged stick pass. It cares about the size and type of discontinuities, not how pretty the surface looks. That’s why a lumpy stick weld can conform while a glassy TIG bead fails — aesthetics are a starting point, never the verdict.

Weld Defects That Ruin an Otherwise Good-Looking Bead

A weld can survive a close visual pass and still be scrap. Surface defects are the warning signs, but the most dangerous flaws often sit just beneath a smooth, even bead. Knowing what each defect looks like, why it forms, and whether it is visible from the outside is how you decide whether to trust a joint. A useful reference is the ESAB welding defects guide, which catalogs the common discontinuity types discussed below.

Surface Defects You Can See

Undercut is a groove melted into the base metal along the weld toe and left unfilled. It shows up as a dark valley or shadow line running beside the bead. Typical causes include high amperage, poor electrode angle, a long arc length, and contamination such as rust.

Overlap happens when molten metal rolls onto cooler base metal without fusing to it. It looks like a rounded lip or shelf sitting on the plate edge rather than blending into it. For a deeper breakdown, see our guide to the overlap welding defect.

Underfill is the opposite problem: the weld face sits below the surrounding base metal, leaving the joint thinner than the plate. Burn-through is a hole melted clean through the root. Arc strikes are stray marks outside the joint that can seed cracks because of their rapid heating and quenching.

Misalignment, or hi-lo, is a fit-up problem where the two surfaces are not flush. Fit-up tolerances are as strict as weld-quality ones, so an offset that exceeds spec can make an otherwise sound bead rejectable.

Porosity: The Pinholes That Weaken the Cross-Section

Porosity is gas trapped in the solidifying metal, and it comes in several shapes: uniform (scattered evenly), cluster (bunched locally), linear (strung in a line), and piping. Piping porosity is a form of porosity with a length greater than its width that lies approximately perpendicular to the weld face. It reduces the weld cross-section and strength and is addressed directly by visual acceptance criteria in AWS D1.1.

Slag Inclusions

Slag inclusions are non-metallic pockets trapped inside the weld, most common in stick, flux-cored, and submerged arc work. They appear as dark, irregular lines or pockets, sometimes revealed only after chipping and brushing. Poor interpass cleaning and a dragged puddle trap them.

Cracks

Cracks are fracture-type discontinuities characterized by a sharp tip and a high length-to-depth ratio. That sharp tip concentrates stress, which is why cracks are normally rejectable in structural codes. They can be longitudinal, transverse, crater, or toe cracks, and many run invisibly beneath the surface.

The Defects That Hide Behind a Pretty Bead

Incomplete fusion and incomplete penetration are the great imposters. A bead can look perfectly uniform while the sidewall or root never actually bonded. Internal cracks behave the same way. None of these are reliably visible from the outside. Catching them takes volumetric testing rather than a flashlight and a trained eye. The lesson is blunt: a beautiful bead is not proof of a sound weld.

Discontinuity vs. Defect: Size, Location, Orientation

Here is the distinction that governs every accept/reject call. A discontinuity is any interruption in the metal’s normal structure. It becomes a defect only when it violates the acceptance criteria of the applicable code. That judgment rests on three measured factors: size, location, and orientation. A small pore away from the root may pass; the same pore aligned perpendicular to the load path may fail. Frameworks like ISO 5817 and AWS D1.1 define these thresholds numerically.

Reject vs. Rework

• Rework: defects like light undercut, minor overlap, or underfill that can be ground out and rewelded while meeting the finish size.
• Reject: cracks, significant lack of fusion, and piping porosity in a structural joint usually demand full removal of the affected section, not a cosmetic patch.

A cosmetic cover pass fixes nothing when the flaw runs deep. For related technique mistakes, see our guides to the overlapping welding technique vs. defect question and to good and bad MIG welds.

Why a Pretty Weld Isn’t Always a Sound Weld: Internal Quality and Testing

Here is the uncomfortable truth about welding: you cannot see the most dangerous defects. A bead can be perfectly uniform, evenly rippled, and the right size and height, and still be a failure waiting to happen. Surface appearance tells you how well the operator controlled the arc: the steadiness of the travel speed, the consistency of the angle, the discipline of the manipulation. It does not tell you whether the weld actually fused to the metal underneath. That gap between what you can see and what actually holds the joint together is the difference between a pretty weld and a sound one.

A beautiful, uniform weld can sit on top of the joint like frosting on a cake rather than melting into it and forming a true metallurgical bond. That is lack of penetration or lack of fusion, and from the outside it can look flawless. The same goes for internal porosity, trapped slag, or cracks that only open under load. Structural integrity depends on what happens below the toe lines, where the weld meets the base metal, which is why appearance and soundness are two distinct questions. A weld that passes the eye test can still fail a stress test.

Where Hidden Defects Hide

For large single-pass fillet welds, the biggest hidden threats are incomplete fusion at the root and slag inclusions. Both sit deep in the joint where no amount of squinting, wire brushing, or careful measuring will reveal them. A clean surface tells you nothing about them. On critical structures, guessing is not an option, which is where good and bad MIG welds diverge well beyond the visible bead shape. The same smooth cap can conceal a sound weld on one part and a rejected one on the next.

The Five Main Non-Destructive Examination Methods

Non-destructive examination (NDE, or NDT) inspects a weld without cutting it apart. Each method has strengths and blind spots, so no single technique catches everything. The trick is choosing the one, or the combination, that matches the defect you are most worried about.

Visual testing is the foundation, and it is the method every other one builds on. Its acceptance criteria trace back to ISO 5817, which defines quality levels B, C, and D for imperfections in fusion-welded joints. ISO 5817 is directly applicable to visual testing, but it does not itself specify the detection methods. That gap is filled by ISO 17635, which correlates quality level with acceptance level for different NDT methods, while ISO 17637 covers visual testing specifically.

Destructive Testing in Qualification

Not every weld is inspected with NDT. During procedure and welder qualification, samples are deliberately destroyed so the joint can be examined from the inside out. Transverse tensile tests (ISO 4136) and bend tests (ISO 5173) expose fusion and ductility problems that visual inspection cannot. A bend test in particular drives cracks and lack of fusion to the surface, revealing weaknesses a flawless bead would happily hide. If the face of a bend opens up or tears, the joint was never truly sound, no matter how good it looked on the bench.

Where to Invest, and How to Read a Report

Match the method to the risk. A decorative rail needs VT; a pressure vessel or lifting frame warrants UT or RT on critical joints. When you receive an inspection report, read the acceptance standard, the quality level, and any recorded indications, not just the pass/fail stamp. Ask what acceptance level was applied and where the indications were found. A defect found once usually points to a process problem worth fixing, whether heat input, travel speed, fit-up, or shielding. Treat inspection as feedback rather than a gate to argue past.

Reading Your Settings and Technique from the Bead

A finished bead is a diagnostic readout. Every hump, dip, and ripple tells you what your machine was doing and what your hands were doing. Once you can read it, you stop guessing and start adjusting with purpose. Our guide to telling good and bad MIG welds apart covers the process-specific version of this skill.

What Heat Tells You

Amperage and voltage decide how much heat enters the joint. Too much heat gives you a flat, wide bead with washed-out edges and, quite often, undercut running along the toes. Too little heat leaves a high, ropey crown sitting on top of the plate, with cold lap and lack of fusion hiding underneath. The metal simply never melted into the parent material. What you actually want is a slightly convex bead that ties into both plates smoothly, with no biting undercut at the toes.

Undercut is commonly caused by excessive amperage, an incorrect electrode angle, or too long an arc length, and prevention starts before you strike an arc: set the machine on scrap metal first and clean the joint properly. On stick, the starting point depends on rod size and position, so dial in your 3/16 E7018 amperage on scrap rather than trusting a label. On wire processes, heat is really a balance between voltage and wire feed speed, which is why matching your MIG welding wire to the machine and material matters.

Wire Feed Speed and Travel Speed

Wire feed speed sets deposition; travel speed sets how that metal is distributed. Feed too fast for your travel speed and the bead piles up, crowns high, and may overlap at the edges. Travel too fast and the bead thins, narrows, and develops a pointed, inconsistent profile with possible porosity. Matching your wire diameter to the joint thickness and position keeps that sweet spot wide and forgiving.

Bead width is itself a workmanship indicator. Under common visual inspection criteria, a GMAW or FCAW bead wider than roughly 10 wire diameters, or a SMAW bead wider than about two electrode widths, counts as excessive. If you’re past that, you’re traveling too slowly or running too hot.

Angle, Manipulation, and Polarity

Work angle controls where the heat lands; travel angle controls where the puddle is pushed. Keep the work angle roughly square to the joint on a fillet, and use a slight drag angle for stick or a slight push for MIG to shape the profile. Uneven leg lengths almost always mean the work angle drifted.

Electrode manipulation changes bead shape too. A tight weave flattens the crown; long, slow oscillation overheats the toes and invites undercut. Rhythm matters more than drama. Polarity is process-specific and often overlooked, and flux-cored wire behaves very differently depending on your polarity setup.

A Simple Diagnostic Flow

1. Observe the symptom — undercut, high crown, wide bead, porosity.
2. Identify the likely cause from the bead’s shape.
3. Adjust one variable only.
4. Re-test on scrap before touching the real part.

For example, elongated piping porosity in flux-cored welding is often corrected by increasing electrode extension, which lowers amperage, or by slightly reducing wire feed speed.

Consistency Beats Luck

Good beads are not accidents. They come from the same settings, the same angle, and the same travel speed, bead after bead. Treat every weld as feedback, and your hands will start producing the readout you want.

Common Mistakes Beginners Make — and How to Fix Them

Every welder’s first beads carry the same fingerprints: a wander here, a blob there, a crater crack at the end. The encouraging part is that nearly all of them trace back to a handful of habits, and each has a concrete fix. Once you can name the mistake, you can drill it out of your hands.

Technique Traps: Speed, Angle, and Stops

Erratic travel speed tops the list. Move too fast and the bead turns thin and crowned with undercut biting the toes; move too slow and you get a fat, convex bead sitting on top of the joint instead of fusing into it. Fix it with rhythm: steady your angle (roughly 10–15° drag or push, depending on process) and let the arc work. If you’re still building the basics, our beginner’s guide to using a wire welder walks through the fundamentals.

Weaving too wide is next. A generous weave looks impressive but spreads heat until the arc can no longer reach the root, killing penetration. Keep stringer beads narrow and only weave when the procedure calls for it. And watch where you stop: crater cracks form at weld terminations, so back up over the end or pause to fill the crater before breaking the arc.

Setup and Prep Mistakes

Wrong polarity is a silent saboteur. Run the leads backward and you lose penetration and gain spatter, especially on flux-cored work — our guide to flux core DCEN vs DCEP explains which way each runs. Contamination is just as common: welding on rust, paint, or a moisture-trapping lap joint is a leading cause of piping porosity, so grind to clean steel and dry the joint before you strike an arc.

Poor fit-up is the third setup killer. Gaps force you to bridge instead of fuse, and misalignment, called hi-lo, creates a step change in cross-section that weakens the joint. Tack carefully, check alignment, and close gaps with a proper lap weld joint technique rather than piling metal over a void. Choosing the wrong electrode for the position (say, a fast-freeze rod where a fill-freeze is needed) finishes the job off.

Symptom → Cause → Fix

The Pretty-Beautiful Trap and Its Opposite

There are two mirror-image errors. The first is chasing a pretty weld while ignoring penetration; a smooth, rippled bead means nothing if the root never fused. The second is assuming an ugly weld must be weak. A slightly ragged but properly fused bead can outperform a gorgeous one that barely bites. Judge fusion, not cosmetics. Weld size and length errors are often simple workmanship issues, and if the welder isn’t measuring the weld before passing it on, undersized or short welds go undetected until someone else catches them.

AWS and ISO both spell out what “acceptable” looks like in visual terms (AWS B1.11 and ISO 5817), and the same references discuss how surface flaws translate to internal quality. The ESAB welding defects guide is a handy second opinion when you’re unsure.

None of this is talent. Good welds are a habit built through repetition and honest self-inspection. Run one clean drill, check it against a gauge, adjust one variable, repeat. Do that long enough and your hands stop making the mistakes your eyes used to miss.

Codes, Standards, and Acceptance Criteria: What ‘Good’ Actually Means

Here’s the uncomfortable truth: a weld isn’t “good” because it looks pretty, and it isn’t “bad” because it has a bit of spatter. Good is a legal and engineering term. It means the weld meets the acceptance criteria written into the code or standard that governs the project. Change the standard, and the same bead can pass or fail.

AWS D1.1: The Structural Steel Benchmark

In North America, structural steel work is usually governed by AWS D1.1, the Structural Welding Code — Steel. One of its clearest rules is that all welds must receive 100% visual inspection. Not a sample, not just the suspicious ones — every weld. The code then applies two families of criteria: visual conditions (surface-breaking flaws like cracks, porosity, and undercut) and dimensional criteria (things you measure, such as leg size, throat, length, and convexity).

A companion document, AWS B1.11, Guide for the Visual Examination of Welds, explains how those checks are carried out and recorded.

ISO 5817: Three Quality Levels

Much of the world works to ISO 5817:2023, which covers fusion-welded joints and defines three quality levels: B, C, and D. Level B is the highest requirement on the finished weld, with the tightest limits on undercut depth, porosity, and bead irregularity. Levels C and D relax those limits. All three describe production and good workmanship, not fitness-for-service on their own.

Picking a level is a real engineering decision. It should reflect design considerations, mode of stressing (static or dynamic), service conditions such as temperature and environment, and the consequences of failure. A fatigue-loaded crane girder in a cold climate is a very different proposition from a low-stress handrail.

Visual vs. Dimensional Criteria

It helps to separate the two. Visual criteria are judgments made with the eye — is there a crack, a crater, visible porosity, or excessive undercut? Dimensional criteria require measurement: leg length, throat thickness, crown height, and weld size. A bead can satisfy one and fail the other, which is why a tape and a gauge belong next to the helmet.

Who Decides, and Who Checks

Final acceptance is normally performed by qualified personnel independent of the welding operation — the person who laid the bead shouldn’t be the only one signing it off. In the U.S., that inspector is often a Certified Welding Inspector credentialed under AWS QC1, the Standard for AWS Certification of Welding Inspectors. When non-destructive testing is involved, personnel are qualified under ANSI/ASNT CP-189. Even a close visual check means staring at bright surfaces, so proper protective eyewear matters for inspectors too.

How to Find Your Governing Criteria

There’s no single universal answer, but the trail is usually easy to follow:

1. Check the drawings and specifications for a referenced welding code.
2. Confirm the quality level, extent of inspection, and any special notes.
3. Verify that welder and inspector qualifications match the code.
4. Record the criteria and results in the shop file.

Documented, pre-agreed acceptance standards are what stop disputes. The customer’s “that’s ugly” and the welder’s “that’s plenty strong” both lose to a written criterion. Keep the standard, the WPS, and inspection records together in an organized workspace — the same way you’d plan welding facilities for efficiency and safety. Agree the standard before the first arc, and you never argue about it afterward.

Conclusion: Building the Habit of Weld Self-Inspection

Reading a weld is a skill you build, not a talent you’re born with. You already know what to look for, so the final step is turning that knowledge into a habit. Before you call any bead finished, run the same mental checklist a seasoned inspector uses.

• Straightness — the bead follows a consistent line down the joint.
• Uniformity — steady width and height, with no thin or bloated sections.
• Smooth toe transition — the edges blend gradually into the base metal rather than biting in or leaving undercut.
• Correct profile — slightly convex, not lumpy or overly crowned.
• Consistent ripples — evenly spaced and regular, a sign of steady travel speed.
• Minimal spatter — little to clean up, a clue that your settings are dialed in.
• No visible porosity or cracks — no glinting pinholes, no hairline fracture at the toe or crater.
• Correct size and length — the leg and throat match the drawing.

That list is your starting point, not the finish line. Visual examination is a fast, inexpensive first line of quality control, but it must be combined with nondestructive testing and, where applicable, destructive testing to confirm structural integrity. A bead that photographs beautifully can still hide lack of fusion or internal porosity, so treat appearance as one leg of a three-legged stool alongside internal soundness and code compliance.

Think of a finished weld the way a doctor reads an X-ray: the surface tells you a lot, but it can’t tell you everything. Your eye catches the obvious, the gauge catches the dimensional, and testing catches the hidden. Used together, they give you a realistic picture. The good news: the tools to self-check are cheap and simple. A fillet weld gauge, a steel ruler, and decent lighting catch dimensional and surface problems before they become rework. Measure rather than guess, and you’ll stop arguing with your own eyes.

Self-inspection also means checking your settings before you weld, not just the bead afterward. If the ripples look cramped or the spatter is heavy, that’s the machine telling you to adjust voltage, wire speed, or polarity rather than pushing through and hoping.

Consistent practice, measured settings, and a disciplined visual check are what separate a reliable welder from one who only gets lucky. So practice on scrap, keep a gauge and ruler handy, and photograph your good and bad beads so you build a personal reference library. When the stakes are high, back up your eye with certification or third-party inspection; partnering with welders certified to AWS standards is one of the easiest ways for a buyer to gain confidence that a fabrication will perform as intended.

The welders whose work is trusted on bridges, pipelines, and pressure vessels aren’t the ones with the steadiest hands. They’re the ones who check, measure, and question every bead before someone else does.

Want to go deeper? Compare your beads against our guide to good and bad MIG welds, learn to spot the overlap defect, dial in flux-core polarity, and set up a safer workspace with our shop planning guide. Then pick up the stinger, strike an arc, and inspect like it’s your name stamped on the part.

Frequently Asked Questions

What are the main characteristics of a good weld bead?

A good weld bead is straight, uniform in width, and centered in the joint, with a smooth slightly convex profile and a smooth toe transition into the base metal. It shows a consistent ripple pattern, minimal spatter, no visible porosity or cracks, and correct size and length for the joint. Appearance is a strong clue, but it is not proof of internal soundness.

Can a good-looking weld still be a bad weld?

Yes. A weld can look flawless on the surface yet contain internal porosity, slag inclusions, incomplete fusion, or cracks, or it may simply sit on top of the joint with little penetration. Confirming structural integrity requires non-destructive testing such as ultrasonic or radiographic inspection, and sometimes destructive testing.

What does undercut look like on a weld?

Undercut appears as a groove or notch melted into the base metal along the edge or toe of the weld and left unfilled. It is often caused by excessive amperage, a long arc length, poor electrode angle, or contamination, and most codes set a limit on its depth.

What are the most common visible weld defects?

The most common visible defects are undercut, overlap, incomplete fusion, slag inclusions, porosity, cracks, and stray arc strikes. Some, like incomplete fusion and internal cracks, may not be visible at all and require NDT to detect.

How do I know if my weld meets code?

You check it against the acceptance criteria in the code or standard specified for your project, such as AWS D1.1 for structural steel or ISO 5817 with its quality levels B, C, and D. Because limits vary by application, the governing specification — not personal opinion — defines what is acceptable.

What is the difference between a discontinuity and a defect?

A discontinuity is any interruption in the typical structure of the material, such as porosity or an inclusion. A defect is a discontinuity that, by its nature or accumulated effect, exceeds the applicable acceptance criteria and makes the part rejectable. In other words, every defect is a discontinuity, but not every discontinuity is a defect.

Does a wider or taller weld mean a stronger weld?

Not necessarily. Excessive reinforcement or an oversized bead wastes material, adds heat and distortion, and can create stress concentrations without adding useful strength. Correct size is defined by the joint design and the applicable acceptance criteria, and it should be measured with fillet gauges rather than judged by eye.

What should I check first when I finish a weld?

Start with the basics: correct size and length, straightness, and uniformity along the joint. Then look closely for undercut, overlap, surface porosity, cracks, spatter, and arc strikes, and confirm the toe lines transition smoothly. Cleaning slag and good lighting are essential before you judge any weld.

Authoritative Sources & Further Reading

• https://pubs.aws.org/Download_PDFS/B1.11M-B1.11-2015-PV.pdf
• https://pubs.aws.org/Download_PDFS/WI-2015-PV.pdf
• https://www.aws.org/magazines-and-media/inspection-trends/it-aug-25-the-answer-is
• https://app.aws.org/mwf/attachments/40/189140/AWSPorosity.pdf
• https://www.iso.org/cms/live/live/en/sites/isoorg/contents/data/standard/08/02/80209.html
• https://webstore.ansi.org/preview-pages/ISO/preview_ISO%2B5817-2023.pdf
• https://esab.com/al/eur_en/esab-university/articles/welding-defects-guide
• https://www.wileymetal.com/what-are-the-characteristics-of-a-good-weld-bead
• https://openwa.pressbooks.pub/lwtechwirefeed/back-matter/visual-inspection-criteria
• https://spot.pcc.edu/welding/PDFs/Weld%20Quality%20Standards.pdf
• https://www.osha.gov/welding-cutting-and-brazing